Combustion apparatus for burning particles of solid or heavy liquid fuel in a fast moving stream



June 15, 1954 E. F. WINTER ETAL 2,680,951

COMBUSTION APPARATUS FOR BURNING PARTICLES OF SOLID OR HEAVY LIQUID FUEL IN A FAST MOVING STREAM Filed April 9, 1948' m w m m Z m, w m w i in m W m N N rm m M, D to cm 1v omw w ow mm 33583 w A\\ .7 B l hhN LII I. {h LAHWMQ m 2M w 8 .I z E; m 5 mm 0mm fi. v m E v S m m OE 02 Patented June 15, 1954 COMBUSTION APPARATUS FOR BURNING PARTICLES F SOLID OR HEAVY LIQUID TENT OFFICE FUEL IN A FAST MOVING STREAM Ernest Frederick Winter, Hove, and Hans August Havemann, Power Jets Woki'ng, England, assignors to (Research and Development) Limited, London, England, a British company Application April 9, 1948, Serial No. 20,036

Claims priority, application Great Britain January 2, 1948 4 Claims. I This invention relates to improvements in combustion systems, and is intended to be more particularly applicable for use with pulverulent solid fuel or heavy fuel oil.

propagation is considered as being of the order of one foot per second at a atmospheric temperature the invention, on the other hand, is especial-- 1y applicable to combustion apparatus for in- It is known in order to facilitate the combus- 5i ternal combustion gas turbine and/or jet propultion of finely divided solid fuel in a fluid, to imsion power units in which the speed of the air part a vortex motion to this fluid, and to introstream in its general direction of flow past a duce the solid material into some part of the combustion zone, calculated on the basis indivortex. cated, might be from to 300 feet per second or A system is also known from British Patent No. 10-: even more, depending on the design, The inven- 338,108 for carrying out chemical and physical tion is further of particular interest in relation to processes involving interaction between fluids or installations which, in common with such power between finely divided solid material and fluids, units, require stabilised burning to be supported for instance, the combustion of finely divided not only by a fast moving air stream but also with: solid fuels, in which vortex motion is imparted to high air/fuel ratios, andv in which stable burn-- a fluid, and the material between Which and the in is required to be maintained at high rates of said fluid interaction is to besecured is introfuel injection with a minimum of pressure loss. duced into some part of the vortex in such a Way Accordin to the invention, in a combustion that the material is suspended with either no system of the character described in which com radial velocity or comparatively low radial vebustion has to be supported by a fast moving airlocity relative to the axis of the vortex and so that stream means are provided for stabilising the the equilibrium paths of the particles of the mateflame produced by the combustion of the fuel. rial under the combined action of centrifugal A further feature of the invention is based on forces and forces tending to move them towards the fact that the velocities and paths of the partithe axis of the vortex are within the chamber in. cles in the vortex chamber are determined largewhich the vortex is produced, while the fluid has a comparatively high velocity relative to the axis so as to obtain relative radial motion between the fluid and the material. with this system the conditions With respect to the speed of the fluid in the vortex and the physical properties of the material introduced thereto are so related that as the reaction proceeds the material will progressively move towards the axis of the vortex; this movement occurs as the parti-- a:

cles shrink. during the reaction and take up an equilibrium path nearer the axis.

A combustion system of the character described (in the last preceding paragraph.) does not in itself provide a flow pattern suitable for use incases in which combustion has to be supported by a fast moving stream of fluid (hereinafter considered as being air), and an object of the invention is toadapt a system of the said; character to the re quirements of such cases. The description fast moving as applied toa combustion-supporting air stream is intended herein to indicate that the speed of the air stream in its general direction of flow past a combustion initiating zone, calculated from the ratio air volume passing in unit time/cross sectional area of the. flow path, is

sufficiently high in relation to the speed of. flame propagation in the fuel-air mixture concerned to have flame extinguishing properties. For hydro-- carbon fuels burning in air the speed of flame Further, in accordanceradial flow at the radial distance.

ly by the form of the boundary walls, because the radialvelocity component of the gas at any particular radial distance from the axis of the vortex depends on the cross-sectional area available for Any desired movement of these particles can thus be ensured by suitable design of the chamber walls and by suitable operating conditions.

Dynamical investigation has shown that certain arrangements have a favourable eifect on.

flow stability and pressure loss. It is in the first Place desirable that the radial velocity component of the gas should be either constant, or should vary continuously from entry to outlet" with varying radial distance from the axis of the vortex; with the object, according to a further feature of the invention the vortex chamber is defined by boundary walls having a form such that the distance between apoint on one wall and a corre- .3 spending oppositely'located point onthe opposite wall measured in the direction of the axis variescontinuously from the periphery up to the outlet with. varying radial distance of the points from this axis and is greater at smaller radii.

Preferably the form of the boundary walls defining the vortex chamber is such that the said axial distance between opposite walls is substantially anexponential. function of the' said radial distance, and conveniently the boundary walls are of. generally outwardly concave form. (In thiscontext outwardly concave or convex means as viewed externally.) A particular case which may have certain advantages for example in respect of pressure loss occurs when the said function is hyperbolic in which case the radial velocity component will be substantially constant at all radii.

In the use of liquid fuels of low volatility, difficulties are often encountered owing to the wide range in the sizes of the droplets produced by the pressure operated jet or air blast atomiser which is generally employed.

A further difficulty is that in the case of some crude liquid fuels the viscosity varies over a wide range for comparatively small changes in temperature, thus substantially altering the degree of atomisation and thence the combustion performance.

With the object of avoiding these disadvantages accordin to a still further feature of the invention the vortex combustion chamber is provided with centrifugal means adapted to introduce fuel particles with a movement of rotation about the axis of the chamber.

By way of example, an embodiment of the invention is described below with reference to the accompanying drawings in which:

Figure l is a transverse section of said embodiment and;

Figure 2 is a section on the line II-II of Figure 1.

Referring to Figure 1, the combustion apparatus comprises a flame tube enclosed by a duct 24 into which is passed a fast moving air stream, as for example, the delivery from the air compressor of a gas turbine engine, and a combustion chamber generally indicated at 4 into which the duct 24 and the flame tube enclosed thereby lead.

The flame tube is generally similar to that de scribed in co-pending United States patent application Serial No. 250,701 in the name of Lloyd, filed October 10, 1951, which is a division of the present application. It comprises a tubular duct 25 which divides the stream entering the duct 24 into two portions, one portion constituting secondary air and passing into the annular space Ila between the two ducts, and the other portion constituting primary air and passing into the interior of the duct 25. The second portion is fur ther divided into two parts by a further tubular duct 23 supported coaxially within duct 25 by a spider 29 at one end and swirl vanes 25a at the other end. Cine part of the air passes through the annular space between ducts 25 and 26 and is given a swirling motion about the axis 1 of the ducts by the swirl vanes 25a. The other part flows partly through the swirl vanes 23a and partly through apertures 21a in a cup shaped stabilising baffie 2?.

Mounted centrally in the flame tube is an air blast burner 23 for crude liquid fuel, the term air blast burner meaning in this case a burner in which atomisation of the liquid fuel is effected by means of an air blast. In the burner shown, liquid fuel is led through pipe 2! while compressed air is led through pipe 22 in order to atomise the fuel.

The stabilising baffle 21 forms on its downstream side a stabilised combustion zone into which the fuel is injected and where it is ignited by means of spark plug 3!. The ignited fuel particles are carried by the swirling air 3 into the combustion chamber 4. It will be appreciated that on entering the combustion chamber, the stream tends, due to its swirling movement, to

fly outwards towards the peripheral part of the chamber and will carry with it the burning particles of fuel.

The first portion of the air stream entering duct 24 flows into the annular space Ha between the ducts 24 and 25. The duct 25 merges into one side wall id of the chamber 4, and the duct 2-! into a wall Ge spaced from the wall id. Ihe air flows between these two walls through a series of swirl vanes 23 arranged as shown in Figure 2 to swirl the air about the axis '8. Part of this air enters the combustion chamber it as secondary air through peripheral inlets 19 which are provided with swirl vanes Hm which accordingly define tangential inlets. The swirl vanes 28 and Mia thus give the air a vortex motion about the axis 1.

Within the chamber 4 the gases circulate around the axis 1 in vortex manner, the fuel particles, which are initially carried outwards by the swirling air stream from the name tube, moving in a circular path and slowly approaching the axis while being burnt until they are either completely burnt or until a very fine ash residue remains which passes together with the combustion products through the axial outlet S formed in the wall 41 of the combustion chamber a.

The air flowing through the space Ila between the walls 4d and dc serves to cool the combustion chamber walls 411. Part of this air does not enter the chamber a but flows through the space llb between the wall t of the combustion chamber and the outer walls 4k, in and 4h, thereby cooling wall M. This air finally passes between swirl vanes 8a arranged in the vicinity of the outlet 8, and mixes with the combustion gases as tertiary air to act as a diluent and coolant.

We claim:

1. Combustion apparatus in which particles of solid or heavy liquid fuel are to be burnt in air supplied as a fast moving stream comprising combustion chamber having two opposed coaxial side walls, one of which is formed with a central inlet for part of the stream, and the other with a central outlet, and means for admitting a further part of the stream peripherally into the chamber with a swirling motion about the axis thereof; an axial tubular extension from said central inlet in the first-mentioned side wall, affording a path leading to said inlet for said first-- mentioned part of the stream; means for form ing a stable zone of combustion within said ex tension; means for injecting fuel into said. zone; and means for causing ignited fuel particles to be carried outwards from said zone into the peripheral part of the combustion chamber.

2. Combustion apparatus in which particles of solid or heavy liquid fuel are to be burnt in air supplied as a fast moving stream comprising a combustion chamber having two opposed coaxial side walls, one of which is formed with a central inlet for part of the stream, and the other with a central outlet, and means for admitting a further part of the stream peripherally into the chamber with a swirling motion about the axis thereof; an axial tubular extension from said central inlet in the first-mentioned side wall, affording a path leading to said inlet for said first-mentioned part of the stream; means for forming a stable zone of combustion within said extension; means for injecting fuel into said zone; and swirlers within said extension disposed to swirl the part of the air stream passing therethrough about the axis thereof, whereby ignited particles of fuel are picked up by the swirling air stream and carried outwards from said zone into the peripheral part of the combustion chamber.

3. Combustion apparatus in which particles of solid or heavy liquid fuel are to be burnt in air supplied as a fast moving stream comprising a combustion chamber having two opposed coaxial side walls, one of which is formed with a central inlet for part of the stream, and the other with a central outlet, and means for admitting a further part of the stream peripherally into the chamber with a swirling motion about the axis thereof; an axial tubular extension from said central inlet in the first-mentioned side wall, ai fording a path leading to said inlet for said firstmentioned part of the stream; a further tubular member coaxially located within said extension and defining therewith an annular passage; means for forming a stable zone of combustion within said further tubular member; means for injecting fuel into said zone; and swirlers within said annular passage disposed to swirl the air passing therethrough about the axis thereof, whereby ignited particles of fuel are picked up by the swirling air stream and carried outwards from said zone into the peripheral part of the combustion chamber.

4. Combustion apparatus in which particles of solid or heavy liquid fuel are to be burnt in air supplied as a fast moving stream comprising a combustion chamber having two opposed coaxial side walls, one of which is formed with a central inlet for part of the stream, and the other with a central outlet, and means for admitting a further part of the stream peripherally into the chamber with a swirling motion about the axis thereof; an axial tubular extension from said central inlet in the first-mentioned side wall, affording a path leading to said inlet for said first-mentioned part of the stream; a jacket spaced from said extension and from said, side wall and defining therewith a path for said further part of the stream; a further tubular member coaxially located within said extension and defining therewith an annular passage; means for forming a stable zone of combustion within said further tubular member; means for injecting fuel into said zone; and swirlers within said annular passage disposed to swirl the air passing therethrough about the axis thereof, whereby ignited particles of fuel are picked up by the swirling air stream and carried outwards from said zone into the peripheral part of the combustion chamber.

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